1. Field of the Invention
The present invention relates to an image processing system that error-diffuses and outputs the image data by SIMD (single instruction multiple data stream) type processor and one sequential processor.
2. Description of the Related Art
Presently, there is know an MFP (multi function peripheral) which is formed as a composite apparatus of an image forming system such as copiers, facsimiles, printers, and scanners. By installing an SIMD (Single Instruction Multiple Data Stream) type processor and auxiliary processor to such an MFP image processor and properly using the two in accordance with the classification of image processing, images are processed at high speed and programmably. Because the SIMD type processor enters multiple data used for processing at a time and processes the multiple data entered in parallel, the SIMD type processor has advantages of processing a large amount of data at a time and processes operations in a short time.
There is one approach of image processing that gives high processing speed by performing processing in parallel at the SIMD type processor and another approach of image processing that gives higher processing efficiency by performing processing by sequential operations. As one example of image processing in which the use of the SIMD type processor is disadvantageous, error diffusion processing can be mentioned. Error diffusion processing is the processing to reflect the difference (error) between the image data value of each pixel and the predetermined threshold value in the image data processing of other pixel when the image data is expressed as an electrostatic latent image on the image bearer or a visual image by toner. In error diffusion processing, the image is handled as the line (pixel line) composed with pixels arranged only in the fast-scan direction as multiple lines arranged in the slow-scan direction. The processing which is advantageous in using the SIMD type processor in error diffusion processing corresponds to error diffusion processing which is carried out between pixels included in pixel lines which are different to each other. In addition, processing in which sequential processing is advantageous corresponds to the error diffusion processing which is carried out between pixels which are included in the same pixel line.
As against to this, as disclosed in the Japanese Patent Application Laid-Open No. 2001-274993, when error diffusion processing is carried out by a conventional image processing unit, error diffusion processing carried out between pixels included in different pixel lines is executed in the SIMD type processor and error diffusion processing carried out between pixels included in the same pixel line is executed at a sequential image data processor which sequentially carries out error diffusion processing.
In the technology disclosed in the above-mentioned literature, error diffusion processing can be used when one-input image data is error-diffused as is the case of black-and-white copiers, and in color copiers, error diffusion processing can be used to form color images by overlapping images on a transfer belt, transfer paper, and other image bearers, but it has a problem of applying error diffusion processing to processing in which YMCK image data nearly simultaneously flow to each of a plurality of photoreceptor drums (image bearers) with a time difference in which transfer paper moves from one photoreceptor to the other.